|Publication number||US6922166 B2|
|Application number||US 10/750,897|
|Publication date||Jul 26, 2005|
|Filing date||Jan 5, 2004|
|Priority date||May 26, 1998|
|Also published as||CA2329861A1, DE69927684D1, EP1082621A1, EP1082621B1, US6111536, US6295019, US6674396, US20020118132, US20040135719, WO1999061936A1|
|Publication number||10750897, 750897, US 6922166 B2, US 6922166B2, US-B2-6922166, US6922166 B2, US6922166B2|
|Inventors||James L. Richards, Larry W. Fullerton, David C. Meigs, Randall S. Stanley, Ivan A. Cowie|
|Original Assignee||Time Domain Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (10), Referenced by (34), Classifications (18), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This is a continuation of U.S. patent application Ser. No. 09/960,278 filed Sep. 21, 2001, now U.S. Pat. No. 6,674,396, which is a continuation of U.S. patent application Ser. No. 09/482,681, filed Jan. 14, 2000, now U.S. Pat. No. 6,295,019, which is a continuation of U.S. patent application Ser. No. 09/083,993, filed May 26, 1998, now U.S. Pat. No. 6,111,536.
1. Field of the Invention
The present invention generally relates to distance measurement, and more specifically to a system and method for distance measurement by inphase and quadrature signals in a radio system.
2. Related Art
Distance measurement systems are required in a wide variety of applications. Surveying, position determination, precision farming and mining are some example applications that require distance measurement systems.
In recent years, various systems for distance measurement systems have been developed. The global positioning satellite (GPS) system operated by the United States Department of Defense, for example, is a highly complex system of determining the position of an object by distance measurement. The GPS system depends on measuring the time-of-flight of signals from three or more orbiting satellite transmitters by a navigation receiver. According to the GPS system, each satellite broadcasts a time-stamped signal that includes the satellite's ephemeris, i.e., its own position. When the mobile unit receives a GPS signal, the mobile unit measures the transmission delay relative to its own clock and determines the distance from the transmitting satellite's position.
Another approach is that employed by the U.S. Navy's TRANSIT system. In that system, a mobile unit performs continuous doppler measurements of a signal broadcast by a low earth orbit (LEO) satellite. The measurements continue for several minutes. The system usually requires two passes of the satellite, necessitating a wait of more than 100 minutes. In addition, because the distance and position calculations are performed by the mobile unit, the satellite must broadcast information regarding its position, i.e., its ephemeris. Although the TRANSIT system is capable of high accuracy (on the order of one meter), the delay required is unacceptable for commercial applications.
Although these systems accurately measure the distance between objects, they are extremely complex, and, more importantly, expensive to implement. For example, both the GPS and TRANSIT systems require multiple satellites, sophisticated receivers and antennas that require hundreds of millions dollars of investments. Also, response times of GPS and TRANSIT systems are typically slow due to their narrow bandwidth. Furthermore, since these systems depend on orbiting satellites, they require an unimpeded view of the sky to effectively perform range measurement. For these reasons, it has been recognized that there is a need for a simple, low cost distance measurement system.
The present invention is directed to a system and a method for distance measurement using a radio system. According to the present invention, a distance is measured by determining the time it takes a pulse train to travel from a first radio transceiver to a second radio transceiver and then from the second radio transceiver back to the first radio transceiver.
The actual measurement is a two step process. In the first step, the distance is measured in coarse resolution, and in the second step, the distance is measured in fine resolution.
In accordance with the present invention, a first pulse train is transmitted using a transmit time base from the first radio transceiver. The first pulse train is received at a second radio transceiver. The second radio transceiver synchronizes its time base with the first pulse train before transmitting a second pulse train back to the first radio transceiver. The second pulse train is received at the first radio transceiver, which then synchronizes a receive time base with the second pulse train.
The time delay between the transmit time base and the receive time base can then be determined. The time delay indicates the total time of flight of the first and second pulse trains. The time delay comprises coarse and fine distance attributes.
The coarse distance between the first and second radio transceivers is determined. The coarse distance represents the distance between the first and second radio transceivers in coarse resolution. An inphase (I) signal and a quadrature (Q) signal are produced from the time delay to determine the fine distance attribute. The fine distance indicates the distance between the first and second transceivers in fine resolution. The distance between the first and second radio transceivers is then determined from the coarse distance and the fine distance attributes.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.
Overview of the Invention
The present invention is directed to a system and a method for distance measurement using a radio system. The present invention can be used to measure the distance between a plurality objects.
Briefly stated, the key to measuring a distance according to the present invention is to precisely measure the time it takes for a single bit to travel from a first radio transceiver to a second radio transceiver. Since in reality it is difficult to transmit and receive a single bit, the distance is measured by determining the time it takes a pulse train to travel from a first radio transceiver to a second radio transceiver and then from the second radio transceiver back to the first radio transceiver. Stated in other terms, the distance is measured by determining the travel time for a complete exchange of data between the first and second radio transceivers.
The actual distance measurement is a two step process. In the first step, the distance is measured in coarse resolution, also referred to as a coarse measurement. In the second step, the distance is measured in fine resolution, also referred to as a fine measurement. Alternatively, the coarse distance and the fine distance can be measured in parallel, or the fine distance can be measured before the coarse distance is measured.
The radios utilized in the present invention may be any one of several types of radios that are capable of transmitting and receiving coded or modulated signals. The modulation can be time or phase modulation, frequency modulation, amplitude modulation, code division multiplex or time division multiplex schemes. It will be apparent to persons skilled in this art that other types of modulation schemes can be easily implemented.
In the following description, an impulse radio system comprising a plurality of transceivers are used for distance measurement. However, it should be understood that impulse radios are chosen as an example only. It will be apparent to persons skilled in the art that the present invention can be implemented easily by other types of radio systems. Furthermore, the present invention also be implemented using optical signals from a laser, light emitting diode (LED) or other types of optical source.
Impulse radio has been fully described in a series of patents, including U.S. Pat. No. 4,641,317 (issued Feb. 3, 1987), U.S. Pat. No. 4,813,057 (issued Mar. 14, 1989), U.S. Pat. No. 4,979,186 (issued Dec. 18, 1990) and U.S. Pat. No. 5,363,108 (issued Nov. 8, 1994) to Larry W. Fullerton. A second generation of impulse radio patents include U.S. Pat. No. 5,677,927 (issued Oct. 14, 1997), U.S. Pat. No. 5,687,169 (issued Nov. 11, 1997) and co-pending application Ser. No. 08/761,602 (filed Dec. 6, 1996) and Ser. No. 09/045,929 (filed Mar. 23, 1998) to Fullerton et al. These patent documents are incorporated herein by reference.
The Present Invention
The preferred embodiments of the invention are discussed in detail below. While specific steps, configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. A person skilled in the relevant art will recognize that other steps, configurations and arrangements can be used without departing from the spirit and scope of the present invention.
Referring now to
The pulse train can be envisioned in both time and space by considering the speed of radio waves in the atmosphere and the frequencies involved. The pulse train is generated by a 10 MHz signal source (described below in detail). Since electromagnetic wave travels at a speed of approximately 100 ft/nano second, a 10 MHz signal source will generate a pulse for each 100 ft of travel by the wave. Consequently, if a 10 MHz oscillator is used to trigger a counter to count the distance traveled by a pulse train, the counter can measure a distance within approximately 50 ft resolution by detecting the rising edge or the falling edge of the clock.
Referring now to
At time t=t1, the second radio transceiver 108 begins to receive the pulse train S1 (indicated by a reference numeral 308). In other words, it takes the pulse train S1 a time t1 to travel from the first radio transceiver 104 to the second radio transceiver 108. The second radio transceiver 108 completes the reception of the pulse train S1 at time t=t2, where t2=(t1+10) micro seconds. The second radio transceiver 108 synchronizes its time base with the pulse train 308. At time t=t3, the second radio transceiver 108 begins transmission of the pulse train S2 (indicated by a reference numeral 312). At time t=t4, the first radio transceiver 104 begins the reception of the pulse train S2 (indicated by a reference numeral 316). The first radio transceiver 104 completes the reception of the pulse train 316 at time t=t5, where t5=(t4+10) micro seconds.
In the example of
Referring now to
Coarse Distance Measurement
Referring now to
The transmit timing signal 510 is received at a counter 512, where the transmit timing signal 510 is divided by N, where N is an integer. The counter 512 outputs a first timing signal 514. In one embodiment, N is 2, and consequently, the first timing signal 514 is a 5 MHz square wave.
The first timing signal 514 is received at a transmit code position counter 516, which counts the number of pulses in the first timing signal 514. In reality, the transmit code position counter 516 counts the number of pulses from the start of the transmission of the pulse train S1 from the first radio transceiver 104. The output of the counter 516 is referred to as a first count value 518, which is a binary number.
Likewise, a receive time base 520 is coupled to a counter 524. The counter 524 receives an output 522 from the receive time base 520 and outputs a receive timing signal 526. In one embodiment, the receive timing signal 526 is a 10 MHZ square wave with a 50% duty cycle.
The receive timing signal 526 is received at a counter 528, where it is divided by N, where N is an integer. The counter 528 outputs a second timing signal 530. In one embodiment, N is 2, and consequently, the second timing signal 530 is a 5 MHz signal.
The second timing signal 530 is received at a receive code position counter 532. The receive code position counter 532 outputs a second count value 534 that indicates the number of pulses counted at the time the transceiver 104 starts to receive the pulse train S2.
The first and second count values (518 and 534, respectively) are received at a latch 540. In one embodiment, the first count value 518 is received at the data input port of the latch 540, while the second count value 534 is received at the “enable” port of the latch 540. The latch 540 outputs a code delay value 542. The code delay value 542 indicates the number of pulses counted between the time the first radio transceiver 104 begins the transmission of the pulse train S1 and the time the first radio transceiver 104 starts to receive the pulse train S2. In other words, the code delay value 542 indicates the sum of the pulses in a pulse train S1 (or S2) and the number of pulses in the time delay. Thus, the number of pulses in the time delay, i.e., the coarse distance, can be calculated by subtracting the number of pulses in a pulse train from the code delay value.
Fine Distance Measurement
The transmit timing signal 510 and the first timing signal 514 are received at a first gate 604. In one embodiment, the first gate is an equivalence gate or an inverted exclusive-or (XOR) gate. Also, in one embodiment, the transmit timing signal 519 is a 10 MHz signal, while the first timing signal 514 is a 5 MHz signal. The first timing signal 514 is also referred to as the TX(I) signal.
The first gate 604 compares the phase of the transmit timing signal 510 to the phase of the TX(I) signal 514 and outputs a TX(Q) signal 606. The duty cycle of the TX(Q) signal 606 is proportional to the phase difference between the transmit timing signal 510 and the TX(I) signal 514.
Turning again to
The TX(Q) signal 606 and the RX signal 530 are received at a third gate 612. In one embodiment, the third gate 612 is an X-or gate. The third gate 612 outputs a Q signal 614. The Q signal 614 has a duty cycle proportional to the phase difference between the TX(Q) signal 606 and the RX signal 530.
The I and Q signals (610 and 614, respectively) are received at a first and a second low pass filter 616 and 620, respectively. The first and second low pass filters can each comprise a resistor and a capacitor. Other types of low pass filters can also be used. The first low pass filter 616 removes ac components from the I signal 610 and outputs an Idc signal 622. The Idc signal 622 represents the average dc value of the I signal 610. Likewise, the second low pass filter 620 removes ac components from the Q signal 614 and outputs a Qdc signal 624. The Qdc signal 624 represents the average dc value of the Q signal 614.
In the present invention, the Idc signal 728 and the Qdc signal 732 are measured as a function of the distance between the first radio transceiver 104 and the second radio transceiver. Stated in other words, a plurality of the Idc signal 728 and the Qdc signal 732 readings are taken as the distance between the first and second radio transceivers (104 and 108, respectively) is varied.
The Idc signal 728 and the Qdc signal 732 are further processed to thereby measure the fine distance. The further processing of the Idc and Qdc signals (728 and 732, respectively) are shown in
Referring now to
Then, the following values are determined:
Then, the octant is determined from Table I.
TABLE I Octant Iz Qz 0 + + 1 + − 2 + − 3 + + 4 − + 5 − − 6 − − 7 − +
Then, an Offset value Ooff is determined from Table II.
TABLE II Octant Offset Value Ooff 0 Qz * S 1 H − Iz * S 2 −Iz * S 3 H − Qz * S 4 −Qz * S 5 H + Iz * S 6 Iz * S 7 H − Qz * S
where H is the distance value of one octant, and S is the slope of the Iz waveform. The offset value spans from 0 to H for each octant as the distance scans across the octant. The fine distance is given by X*H+Ooff, where X is the octant number. Then the coarse distance is adjusted as follows.
Finally, the fine distance is added to the adjusted coarse distance to thereby calculate the total distance.
Applications of the Present Invention
The following applications are described as a few selected examples. It will become apparent to persons skilled in the art that the present invention can be utilized in many other applications.
(1) Position Determination
The present invention can be used to determine the position of one or more objects. The objects have fixed locations or can be moving with respect to each other. In one embodiment, a plurality of radios can be combined to provide the position of a desired object (or one or more radios). The actual position can be calculated by triangulation, direction finding antennas or other techniques that are well known in the art. A position determination system based on the present invention can be installed in a mobile phone system (e.g., cellular phone, PCS phone) to thereby provide position information to mobile phone users.
A position determination system built in accordance with the present invention would be more reliable than similar systems based on global positioning satellites (GPS), because the radios in the present invention can be better controlled to provide the desired coverage. Also, such a system based on radios will be more accurate because of the inherent sub-centimeter link accuracy for each link. Also, a position determination system according to the present invention would be superior over an optical system due to its omni-directional antenna pattern and its greater dust and rain resistance.
(2) Distance or Range Measurement for Surveying
The present invention can be utilized for accurate range measurements with sub-centimeter resolution, thereby making the present invention a low cost and less complex alternative to the GPS systems used for high resolution range measurement. Furthermore, the present invention can be used where GPS is unavailable or intermittent, such as in urban areas, in forests or in canyons. Also, the concurrent voice channel available can be used for simultaneous distance measurement and voice communications.
(3) Precision Farming
The present invention can be used to automatically or semi-automatically guide farm equipment with sub-centimeter repeatability and precision. It would not be dependent on satellite constellation as GPS and would be more immune to weather than optical systems. The concurrent data channel can be used for control commands or voice communications.
Open and underground mining involves operations where GPS is intermittent or not available at all. The present invention can provide reliable and continuous service in these situations. In addition, the multipath immunity of the ultra-wideband (UWB) radio system has been demonstrated to provide excellent communications in underground tunnels where carrier based communication systems fail.
(5) Marine Navigation
The present invention can provide ship to shore link as well as precise full duplex communications. Also, two radios, one at each end of a ship can provide precision docking information.
(6) Asset Tracking
Large shipyards and warehouses have a need for dynamic asset tracking. A system based on the present invention can transmit ID tags and provide link distance as part of an asset position tracking system.
(7) Aircraft Landing
The high precision and rapid measurement rate available from the present invention makes it an ideal sensor for an aircraft precision landing device. Its independence from GPS and immunity to weather make it extremely reliable. Also, multipath immunity makes the present invention insensitive to local propagation conditions and thus extremely portable. As a result, a precision aircraft landing device built in accordance with the present invention can be set up at remote fields in a matter of hours.
(8) Aircraft Collision Avoidance
A collision avoidance system could be built using the present invention. In one embodiment, low cost transponders built according to the present invention can be installed in aircrafts. A simple link between two aircrafts that indicates a steady closing velocity suggests a collision course. A course between two aircraft at a steady velocity that is not a collision course will show a decreasing closing velocity. If additional sensor data is provided on the link, such as altitude, compass, or GPS coordinates, then faster and more accurate predictions of potential collision could be made. The system can operate with or without GPS or interface with ground equipment.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. Thus the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
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|U.S. Classification||342/125, 342/194, 342/52, 342/195, 342/53, 342/54, 342/118|
|International Classification||G01S13/08, G01S13/86, G01S13/76|
|Cooperative Classification||G01S13/87, G01S13/913, G01S13/765, G01S13/08, G01S13/76|
|European Classification||G01S13/08, G01S13/86, G01S13/76|
|Jan 26, 2009||FPAY||Fee payment|
Year of fee payment: 4
|Mar 19, 2011||AS||Assignment|
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:TIME DOMAIN CORPORATION;REEL/FRAME:025983/0646
Owner name: TDC ACQUISITION HOLDINGS, INC., ALABAMA
Effective date: 20101231
|Dec 27, 2012||FPAY||Fee payment|
Year of fee payment: 8